The present invention relates to a method of manufacturing a wireless suspension blank used in a hard disc drive (hereafter called xe2x80x9cHDDxe2x80x9d) as a data storage device and others.
Prior art concerning a method of manufacturing the above-mentioned member for electric parts is mentioned in Japanese Patent Laid-open 2000-49195, in which a method of manufacturing a wireless suspension blank used for HDD is not concretely explained. However, a method of manufacturing a member for electric parts is disclosed as follows.
In the manufacturing method, a three-layered laminate composed of a polyimide resin film and metallic foils laminated on both sides of the polyimide resin film is used as a laminate. In the method, resist patterns are formed on the metallic foils laminated on both sides of the polyimide, respectively, and the two metallic foils are treated at the same time with etching solution. Thereafter, resist patterns are removed from the two metallic foils, and then plasma etching of the polyimide resin film is done through one metallic foil etched as a mask to form the polyimide resin film into a pattern. Thereafter, the metallic foil used as a mask is removed from the polyimide resin film. As a result, a member for electronic part can be obtained which is composed of a laminate of the polyimide resin film formed into a pattern and the metallic foil formed into a pattern. This effect is that low-cost production is possible since reproduction is one time and a high quality product can be obtained in which a pattern of polyimide resin film is put on a pattern of metallic foil with a high positioning accuracy.
However, the above-mentioned method has a first problem in that the three-layered laminate used is high-priced.
Further, the above-mentioned method has a second problem in that the working of metallic foil is difficult since same requires a finer working accuracy, since wet etching is employed using etching solution applied to the metallic foils laminated on both sides of the polyimide resin film of three-layered laminates.
Further, the processing of polyimide film as the insulating layer has a problem that since it is carried out by the dry etching method, such as the plasma etching method, the product made by dry etching is high-priced.
Further, polyimide film has a fourth problem in that applying low-cost wet etching instead of dry etching is difficult.
In order to decrease the curve of a laminate used in the above-mentioned method, the coefficient of thermal expansion of the metallic layer is necessarily equalized with the coefficient of thermal expansion. Accordingly, it is desirable to use a low-expansible polyimide resin and others as an insulating layer.
However, since low-expansible polyimide does not have, in general, thermoplastic properties, low-expansible polyimide is deficient in adhesive properties for bonding to the metallic layer such that obtaining sufficient adhesive strength of the polyimide to the metallic layer is difficult. It is known to use thermoplastic polyimide resin and epoxy resin having good adhesive properties for bonding to the metallic layer as an adhesive layer layered between a metallic layer and low-expansible polyimide. Polyimide resin is used in, for example, adhesives used as a part of an insulating layer in a laminate of a wireless suspension blank, from the necessity that reliability on high insulating property should be maintained. In order to give insulating properties to polyimide resin, thermoplastic properties are given in general to polyimide resin. However, if the flexible structure giving thermoplastic properties is introduced into a frame of polyimide resin, there is a tendency for chemical resistance of the polyimide resin to be increased. Accordingly, there is a tendency for etching-ability to be decreased in the wet,process so that the etching rate of polyimide is away from the etching rate of the core-insulating layer, wherein xe2x80x9cetching ratexe2x80x9d means the amount of the decrease of thickness produced by etching per hour.
When a core-insulating layer is made of low-expansible polyimide, an adhesive layer is made of polyimide with adhesive properties and the core-insulating layer and the adhesive layer are combined so that an insulating layer made of a plurality of layers (for example, adhesive layer core-insulating layer/adhesive layer, adhesive layer/core-insulating layer) is formed. If etching by the wet process is given to the insulating layer of a plurality of layers, there is a tendency for etching-ability to be decreased, since the adhesive layer shows a tendency toward higher chemical resistance. However, since the core-insulating layer is apt to be etched, etching of the whole insulating layer does not proceed uniformly so that the shape of etching is not uniform. The goals of adjusting etching rates of a core insulating layer and an adhesive layer of an insulating layer in a laminate for a wireless suspension blank to a suitable amount, and to improve the adhesive properties of the adhesive layer conflict with each other, and so the coexistence of the former with the latter is difficult.
Therefore, with respect to a conventional laminate for a wireless suspension blank, the etching condition in the wet process is not known, and setting of a uniform etching condition is difficult. Accordingly, etching of the insulating layer is achieved by the dry process using plasma or laser etching in the present conditions.
The present invention was developed considering the above-mentioned background. The present invention aims at the provision of a method of manufacturing a wireless blank in which the working of a wireless suspension blank is possible with high accuracy.
The present applicant filed previously the application (Japanese Patent Application No. 186564 of 2000) concerning a laminate for a wireless suspension blank being an object of the present invention, in which wet etching is made accurately at a low-cost. Its content is as follows. Namely, this application says that an insulating layer is formed of two or more resin layers and a good shape of etching can be obtained, if the ratio of higher etching rate to a lower etching rate of the respective layers of the insulating layer is between 6:1 and 1:1, and preferably between 4:1 and 1:1. Accordingly, in the present application, an insulating layer having the above-mentioned constitution is employed so that good etching shape can be obtained in the wet etching process of an insulating layer.
Accordingly, a first method of manufacturing a wireless suspension blank according to the present invention is a method of manufacturing a wireless suspension blank in which a three-layered laminate formed of a metallic layer having a spring property and a conductive layer laminated on the metallic layer through an electrically insulating layer is used, wherein the laminate comprises the insulating layer formed of a core-insulating layer and adhesive layers applied on both sides of the core-insulating layer and with the ratio of higher etching rate to a lower etching rate of the respective layers of the insulating layer being between 6:1 and 1:1, preferably between 4:1 and 1:1, and the method comprises the steps of: a step for processing the metallic layer and the conductive layer by the photo etching method, respectively; a step for forming a resist pattern for processing the insulating layer; and a step for processing the insulating layer through the resist pattern by the wet etching method.
In the present invention, it is preferable to use a laminate having at least 300 g/cm of the adhesive strength of the adhesive layer to the metallic layer, the conductive layer and the core-insulating layer.
Further, it is preferable to use a laminate having the ratio of the thickness of the core-insulating layer to the thickness of the adhesive layer of 4:1 at maximum.
It is preferable to use a laminate in which at least one layer forming an insulating layer is made of polyimide resin or a laminate in which the whole layers forming an insulating layer are made of polyimide resin.
A second method of manufacturing a wireless suspension blank is a method of manufacturing a wireless suspension blank in which a two-layered laminate formed of a metallic layer having the spring property and a conductive layer laminated on the metallic layer through an electrically insulating layer is used, wherein as the laminate comprises the insulating layer formed of a core-insulating layer and adhesive layers and with the ratio of higher etching rate to a lower etching rate of the respective layers of the insulating layer of between 6:1 and 1:1, preferably between 4:1 and 1:1, and the method comprises the steps of: a step for processing the metallic layer by the photo etching method; a step for forming a wiring part on the insulating layer by the semi-additive method; a step of forming a resist pattern for processing the insulating layer; and a step for processing the insulating layer through the resist pattern by the wet etching method.
In the present invention, it is preferable to use a laminate having at least 300 g/cm of the adhesive strength of the adhesive layer to the metallic layer and the core-insulating layer.
Further, it is preferable to use a laminate having the ratio of the thickness of the core-insulating layer to the thickness of the adhesive layer of 4:1 at maximum.
It is preferable to use a laminate in which any or the two of the core-insulating layer and the adhesive are made of polyimide resin.